With 13 years of experience and an outstanding record of performance, the HIV Prevention Trials Network (HPTN) Laboratory Center (LC) is optimally positioned to support the HPTN in 2013 and beyond. As part of the HPTN Leadership Group, the LC will help shape the network's scientific agenda. The HPTN LC will oversee laboratory activities at study sites; perform Quality Control/Quality Assurance (QA/QC) and specialized testing for HPTN protocols; evaluate and validate assays for use in HPTN protocols; develop novel assays to achieve study objectives; and perform ancillary studies related to HIV prevention. The HPTN LC has comprehensive QA/QC, Virology, and Pharmacology Cores, with Support Laboratories in other key areas (Sexually Transmitted Diseases, Microbiology, Immunology, and Toxicology). The HPTN LC has extensive experience supporting HIV prevention trials in the United States, South America, Asia, and Africa and has led efforts to harmonize laboratory procedures across networks and in other groups. The HPTN LC has supported HPTN protocols evaluating behavioral, biomedical, and structural interventions for HIV prevention, often delivered in combination in a wide range of settings and non-traditional venues. This includes observational, Phase I, Phase II and Phase III studies, with interventions delivered to HIV uninfected individuals, HIV-infected individuals, couples, cohorts, and communities. HPTN study populations include adolescents, women, men who have sex with men, serodiscordant couples, injection drug users, and individuals with acute HIV infection, with some trials enrolling >50,000 participants. The Specific Aims of the HPTN LC are: Aim 1: To provide leadership, expertise, and laboratory support to the HPTN; Aim 2: To support site laboratories and ensure the quality of HPTN laboratory results; Aim 3: To advance HIV prevention science through assay development and biomedical research. A strong and effective LC is particularly important in the HPTN because of the vast international scope, diversity, and complexity of HIV prevention trials. This award will enable the HPTN to continue its mission to identify effective strategies for HIV prevention that will help end the HIV/AIDS epidemic.